Wireless communication systems keep evolving to meet the needs for providing continuous and faster access to a data network. In order to meet these needs, wireless communication systems may use multiple carriers for the transmission of data. A wireless communication system that uses multiple carriers for the transmission of data may be referred to as a multi-carrier system. The use of multiple carriers is expanding in both cellular and non-cellular wireless systems.
A multi-carrier system may increase the bandwidth available in a wireless communication system according to a multiple of how many carriers are made available. For instance, a dual carrier system will double the bandwidth when compared to a single carrier system and a tri-carrier system will triple the bandwidth when compared to a single carrier system, etc. In addition to this throughput gain, diversity and joint scheduling gains may also be expected. This may result in improving the quality of service (QoS) for end users. Further, the use of multiple carriers may be used in combination with multiple-input multiple-output (MIMO).
By way of example, in the context of third generation partnership project (3GPP) systems, a new feature called dual cell high speed downlink packet access (DC-HSDPA) has been introduced in Release 8 of the 3GPP specifications. With DC-HSDPA, a base station (which may also be referred to as a Node-B, an access point, site controller, etc. in other variations or types of communications networks) communicates to a wireless transmit/receive unit (WTRU) over two downlink carriers simultaneously. This not only doubles the bandwidth and the peak data rate available to WTRUs, but also has a potential to increase the network efficiency by means of fast scheduling and fast channel feedback over two carriers.
For DC-HSDPA operation, each WTRU is assigned two downlink carriers: an anchor carrier and a supplementary carrier. The anchor carrier carries all physical layer dedicated and shared control channels associated with transport channels such as the high speed downlink shared channel (HS-DSCH), the enhanced dedicated channel (E-DCH), and the dedicated channel (DCH) operations. Such physical layer channels include, by way of example, the fractional dedicated physical channel (F-DPCH), the E-DCH HARQ indicator channel (E-HICH), the E-DCH relative grant channel (E-RGCH), the E-DCH absolute grant channel (E-AGCH), the common pilot channel (CPICH), the high speed shared control channel (HS-SCCH), and the high speed physical downlink shared channel (HS-PDSCH), and the like). The supplementary carrier may carry a CPICH, an HS-SCCH and an HS-PDSCH for the WTRU. The uplink transmission remains on a single carrier in the current system. The high speed dedicated physical control channel (HS-DPCCH) feedback information is provided on the uplink carrier to the Node-B and contains information for each downlink carrier.
FIG. 1 shows the medium access control (MAC) layer structure for DC-HSDPA operation in a 3GPP context. The MAC-ehs entity includes one hybrid automatic repeat request (HARQ) entity per HS-DSCH transport channel. This implies that HARQ retransmissions may take place over the same transport channel which somewhat restricts the benefit of frequency diversity potentially brought by the use of more than one carrier if each HS-DSCH transport channel has a fixed mapping to physical channel resources. However, it has been suggested that the mapping between an HS-DSCH and physical resources (e.g., codes and carrier frequencies) may be dynamically modified in order to provide a diversity benefit.
As mentioned above, multi-carrier transmissions increase the throughput and efficiency of the downlink. However, in the uplink, physical layer channels are carried using a single carrier. Therefore, a need exists for a method and apparatus for handling uplink transmissions using multiple uplink channels.